1. Field of the Invention
Theophylline (1,3-dimethylxanthine) is a drug commonly used in the treatment of asthma, hypertension and nephrotic edema. At elevated plasma levels, theophylline will sometimes produce nausea and serious toxic effects may occur at high plasma concentrations ranging from about 25-70 .mu.g/ml. Serum theophylline shows considerable individual variation in patients, due to wide differences in the extent of metabolism and secretion as well as fluctuations during dosing intervals in the rate of absorption and distribution. With infants, the problems are further exacerbated, due to the infants low body fluid level.
In view of the serious side effects as a result of elevated serum theophylline levels, it is important that sensitive techniques be provided for monitoring theophylline levels. The technique should be rapid, accurate, and readily distinguish theophylline from its normal metabolites and widely prevalent analogs, such as xanthine and caffeine.
2. Description of the Prior Art
U.S. Pat. Nos. 3,690,834, 3,817,837, 3,850,752, and 3,766,162, and the references cited therein, describes a series of different immunoassays. The disclosure of U.S. Pat. No. 3,817,837 describing a homogeneous enzyme immunoassay is incorporated herein by reference. Synthesis of xanthine derivatives may be found in Advances in Heterocyclic Chemists 1966 Vol. VI, Lister et al, Rev. Pure & Applied Chem. (Australia). See also U.S. Pat. Nos. 2,517,410 and 2,673,848, as well as Holmes and Leonard, J. Org. Chem. 41 568(1976) and Cavalieri et al, J. Am. Chem. Soc. 76, 1119 (1954) for the preparation of xanthene derivatives. Rasmussen and Leonard, J. Am. Chem. Soc. 89 5439 (1967) discloses the use of pivaloyloxymethyl as a protecting group.